Studies in neurological patients with brain lesions suggest that the normal process of retrieving words which denote concrete entities depends in part on multiple regions of the left cerebral hemisphere, located outside classic language areas, in higher-order association cortices. The findings also indicate that, at the level of large-scale systems, there appears to be an intriguing and principled relationship between the anatomical region and the kind of item being named. These findings open the possibility of investigating further the nature of the lexicon and its neural underpinnings, and that is the aim of this project, focused on the issue of lexical retrieval pertaining to concrete entities. We will test three principal hypotheses in a series of [150]H2O PET experiments conducted in 60 normal native English speaking adults. We will begin by testing the idea that the retrieval of words denoting concrete entities pertaining to diverse conceptual categories depends on anatomically separable regions. We will then test the idea that such regions are the same regardless of the sensory mode (e.g., visual [pictures] versus auditory [associated sounds]) of presentation of the concrete entities to be named. Finally, we will test the idea that the same regions operate not only for, retrieval of words, given the concepts, but also for the retrieval of concepts, given the words. In addition to contributing to a better understanding of the neural basis of language processing, the findings are also likely to contribute to the understanding of the neural architectures which subserve cognition, at large-scale systems level, and will have a direct application in the diagnosis and management of disorders of communication and memory.